Semiconductor devices include transistors. A transistor may modulate a current flowing through it in response to an input signal. One example of a type of a transistor is a field effect transistor (FET). An FET may change the characteristics of a channel in response to the input signal. The input signal affects the characteristics of the channel such as the carrier concentration and the carrier type. By affecting the characteristics of the channel, the input signal may modulate current flowing through the channel, and hence, flowing through the transistor. Typically, such a transistor may include a source and a drain coupled to the channel. A gate receives the input signal to modulate the channel.
Heterostructure FETs (HFETs) are FETs manufactured out of at least two different semiconductor materials, hence a ‘hetero’ structure rather than a homogenous one. The use of zinc oxide (ZnO) has promising potential for sensors. Zinc oxide reacts to its surrounding environment. The carrier concentration in the channel of the HFET may be controlled by the surrounding environment, allowing the zinc oxide to act as a ‘chemical gate.’
However, bare zinc oxide surfaces may have stability issues that result in its difficulties to withstand typical environments in which gas or liquid sensors operate. Additionally, zinc may escape from the surface, contaminating or detrimentally affecting biosensors.